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Rev

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Activate the Laser Gates

In a secret lab corridor, there are emitters and gates: A number represents a laser emitter with a certain frequency, a 0 represents an inactive gate. If two emitters of the same frequency face each other with only inactive gates (0) in between, their beams meet and activate the entire stretch of gates in between. But if any other emitter is in the way, the beam is blocked.

Your task

Write a program that simulates the beam activation.

Input

A list/array of nonnegative integers.

Output

The transformed list/array, with activated gates.

Winning Criteria

The shortest correct program (measured in bytes) wins. In the event of a tie, the earliest posted answer wins.

Sample data

Example 1 (Simple case)

[0,2,0,0,2]         
→ [0,2,2,2,2]

Example 2 (Gate between emitters)

[0,2,0,1,0,2]       
→ [0,2,0,1,0,2]

Example 3 (A more complex example)

[0,2,0,2,5,0,0,5,1] 
→ [0,2,2,2,5,5,5,5,1]

Example 4 (Consecutive emitters)

[3,0,0,3,0,3]       
→ [3,3,3,3,3,3]

Answer*

# JavaScript (ES6), 48 bytes



    a=>a.map(p=(v,i)=>v|a.find(v=>i--*v<0)!=p?p=v:p)

[Try it online!][TIO-memvva5e]

[JavaScript (Node.js)]: https://nodejs.org
[TIO-memvva5e]: https://tio.run/##bY3NDoIwEAbvPgXeWlMKhXAxbn0Q08OGH1MDdCOmJ9@9SiNGIjvJXr5M5oYep/pu6ZGOrmlDBwFBoxyQGAHzwnLQ/omys2PDPGibpgd/yvke6Ezgj8RD7cbJ9a3s3ZV17JKLQuRvCsN5slyWJXGImN2motbSoizDtlSIKtYqoWb1t1N9UH9qGZX5l@teKb6Y8AI "JavaScript (Node.js) – Try It Online"

### Commented

    a =>            // a[] = input array
    a.map(p =       // start with p non-numeric
    (v, i) =>       // for each value v at index i in a[]:
      v |           //   if v is not zero
      a.find(v =>   //   or the first non-zero value in a[]
        i-- * v < 0 //   at an index higher than i (1)
      ) != p ?      //   is not equal to p (2):
        p = v       //     set p to v
      :             //   else:
        p           //     use the current value of p
    )               // end of map()

*<sub>(1) The expression `i-- * v < 0` is true if and only if `i` is negative and `v` is non-zero.  
(2) If there's no such non-zero value at all, `find()` returns undefined, which cannot be equal to `p`.</sub>*

If this is an answer to a challenge…

…Be sure to follow the challenge specification. However, please refrain from exploiting obvious loopholes. Answers abusing any of the standard loopholes are considered invalid. If you think a specification is unclear or underspecified, comment on the question instead.
…Try to optimize your score. For instance, answers to code-golf challenges should attempt to be as short as possible. You can always include a readable version of the code in addition to the competitive one. Explanations of your answer make it more interesting to read and are very much encouraged.
…Include a short header which indicates the language(s) of your code and its score, as defined by the challenge.

More generally…

…Please make sure to answer the question and provide sufficient detail.
…Avoid asking for help, clarification or responding to other answers (use comments instead).

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